A silicon-based, sequential coat-and-etch process to fabricate nearly perfect substrate surfaces.

For many thin-film applications substrate imperfections such as particles, pits, scratches, and general roughness, can nucleate film defects which can severely detract from the coating's performance. Previously we developed a coat-and-etch process, termed the ion beam thin film planarization process, to planarize substrate particles up to approximately 70 nm in diameter. The process relied on normal incidence etching; however, such a process induces defects nucleated by substrate pits to grow much larger. We have since developed a coat-and-etch process to planarize approximately 70 nm deep by 70 nm wide substrate pits; it relies on etching at an off-normal incidence angle, i.e., an angle of approximately 470 degrees from the substrate normal. However, a disadvantage of this pit smoothing process is that it induces defects nucleated by substrate particles to grow larger. Combining elements from both processes we have been able to develop a silicon-based, coat-and-etch process to successfully planarize approximately 70 nm substrate particles and pits simultaneously to at or below 1 nm in height; this value is important for applications such as extreme ultraviolet lithography (EUVL) masks. The coat-and-etch process has an added ability to significantly reduce high-spatial frequency roughness, rendering a nearly perfect substrate surface.

Diffraction-limited large x-ray optics.

It is shown that the technologies required to produce large normal-incidence multilayer x-ray mirrors with diffraction-limited resolution are now available. Applications of these mirrors in x-ray astronomy and x-ray lithography are discussed.

Refractive index of amorphous carbon near its K-edge.

The refractive index of the amorphous carbon layers inside multilayer soft x-ray mirrors is derived in the lambda = 42-58-A wavelength range by measuring the shift in the Bragg angle caused by refraction. Reflectivity curves are measured with a reflectometer behind a zone plate monochromator at the National Synchrotron Light Source. The monochromator consists only of a freestanding zone plate of gold and an exit slit and is free of any of the contamination problems often found in monochromators that contain mirrors.

Large area coatings with uniform thickness fabricated in a small vacuum chamber.

Evaporative atom reflections from chamber walls are used to enhance direct line deposition. Interfacial surface roughness is reduced by depositing at near normal incidence. Film thickness depends on the mass of the evaporant and the chamber geometry.

Fabrication and testing of large area multilayer coated x-ray optics.

We discuss the procedures developed for the production and testing of multilayer x-ray mirrors on large figured optical surfaces. Methods which are generally useful for characterizing the performance of such optics are presented, as well as specific results from the production of a 25-cm diam Ritchey-Chretien telescope for a wavelength of lambda = 63.5 A. The latter is a two-mirror system, which places additional stringent requirements upon the accuracy and quality of the coatings.

Graded-index AR surfaces produced by ion implantation on plastic materials.

The damage tracks of high energy ions in dielectric materials can be etched until overlapping conical etch pits are obtained. If the depth of the pits is >lambda/2, an effective graded-index layer with very low reflectivity is obtained. Broadband antireflection treatment achieving reflectivities of <10(-4) has been applied to plastics like Lexan and Mylar.

High resolution microchemical analysis using soft X-ray lithographic techniques.

High resolution x-ray lithographic studies of cells from chick embryo hearts dried by the CO2 critical point method have been made with soft x-ray radiation of different wavelengths. A marked difference in the relief replica in polymethyl methacrylate (PMMA) resulting from the differential absorption by the dried cells of carbon K alpha radiation at 4.48 nm and broad band synchrotron radiation (SR) with lambda is greater than 1.5 nm demonstrates the potential usefulness of the technique in making high resolution (approximately or equal to 10 nm) chemical identification of the constitutents which make up the various parts of the cell.

Transmission microscropy of unmodified biological materials: comparative radiation dosages with electrons and ultrasoft x-ray photons.

The minimum radiation dosage in a specimen consistent with transmission microscopy at resolution d and specimen thickness t is calculated for model specimens resembling biological materials in their natural state. The calculations cover 10(4)-10(7) eV electrons and 1.3-90 A photons in a number of microscopy modes. The results indicate that over a considerable part of the (t,d)-plane transmission microscopy on such specimens can be carried out at lower dosage with photons than with electrons. Estimates of the maximum resolutions obtainable with electrons and photons, consistent with structural survival of the specimen, are obtained, as are data on optimal operating conditions for microscopy with the two particles.

High-resolution soft x-ray microscopy.

X-ray micrographs of biological materials have been obtained with a resolution better than 100 angstroms by using x-ray resist as the recording medium. A high-resolution scanning electron microscope with a short-focal-length final lens, operating in the "low-loss" mode, is used to make the smallest features in the x-ray replica visible.

Potential operating region for ultrasoft x-ray microscopy of biological materials.

Calculations are presented which indicate an extensive suboptical region in the microscopy of biological materials in their natural state which is accessible to ultrasoft x-ray transmission microscopy. Throughout most of the region, radiation dosage levels to the specimen are lower than in electron microscopy.

X-ray microscopy of biological objects with carbon kappa and with synchrotron radiation.

X-ray micrographs of biological objects have been obtained with a resolution better than 1000 angstroms by using poly(methyl methacrylate) x-ray resist and carbon Kalpha or synchrotron radiation. Synchrotron radiation allows short exposure times; storage rings especially designed as radiation sources and improved x-ray resists would make exposure times under 1 second possible.

Reflective multilayer coatings for the far uv region.

Progress in the field of reflective multilayer coatings for the wavelength region between 50 A and 2000 A is reviewed. All the coatings contain absorbing materials, absorption losses are minimized by positioning strongly absorbing materials into the nodes of the standing wave inside the coating. Above lambda = 1200 A, ideal coatings with a reflectivity approaching 100% are theoretically possible; the theoretical predictions have been confirmed for coatings up to six layers at wavelengths around 2000 A. Below lambda = 1000 A, no absorption-free material is available that can be used as a spacer layer to cover the antinodes of the standing wave field. This limits the theoretically obtainable reflectivity. However, even at the shortest wavelength a reflectivity of 30% is still possible. Experimental results have been obtained for wavelengths between 100 A and 200 A for coatings up to nine layers. Discrepancies between experiment and theory can be explained as due to insufficient knowledge of the optical constants of the films used. Extensive future work on the optical constants of materials and their dependence on film thickness and deposition conditions is required for further improvement.

Interference filters for the ultraviolet and the surface plasmon of aluminum.

It is shown that (Al-MgF(2))-interference filters of better performance than have been predicted and obtained previously are possible in the uv below 2500 A. Experimental results are given for conventional filters of first and higher order and for new filter designs that use multilayer structures for the two mirrors of the filter. All discrepancies between theoretical and experimental results are explained by a coupling of light into the surface plasmon of aluminum via a surface roughness of the MgF(2) films.

High resolution lenses for optical waveguides.

A mode index lens and a lens formed by a spherical depression in the substrate of the waveguide have opposite aberrations and can be combined in an element with considerably reduced aberrations. Only small differences in the mode index are required for the optimum combination.

Broadening of short light pulses by many reflections from multilayer dielectric coatings.

The broadening of short light pulses which are reflected from multilayer dielectric mirror coatings is calculated. The case when a pulse is reflected many times is treated in detail. The quarter-wave stack is the design for minimal pulse broadening. The broadening after many reflections is mainly due to the phase variations close to the edge of the reflection band of the coating. The shortest output pulses are obtained if only the center part of the reflection band of the mirror is used; an input pulse which contains only this part of the spectrum produces a much shorter output pulse than a delta-function input. Output pulses as short as 10(-13) sec are possible for typical mirror coatings and one-thousand reflections. The influence of errors in the fabrication of a coating on the calculated results is discussed.